1. Field of the Invention
The present invention relates to an air cushion mechanism which can stop a piston at an arbitrary set position in a pneumatic cylinder in a buffering manner.
2. Description of the Related Art
As an air cushion mechanism for stopping a piston in a pneumatic cylinder in a buffering manner, those for giving a cushion action to a piston by temporarily having compressed air in a discharge-side pressure chamber remain have been known as disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2006-46500), for example. This type of air cushion mechanism has the discharge-side pressure chamber in a cylinder chamber opened into the air through a throttle valve in the vicinity of a dead end of a piston stroke so as to temporarily seal the discharge air in the discharge-side pressure chamber and to stop the piston in a buffering manner. This is advantageous in that a large impact absorbing capability can be exerted since an impact at the stroke end is absorbed using compressibility of air remaining in the discharge-side pressure chamber.
As the above air cushion mechanism, in the vicinity of the dead end of the piston stroke, means for switching a main discharge system having performed discharge of the compressed air from the cylinder chamber to a cushion discharge system for discharging it to the air from the discharge-side pressure chamber through a throttle valve is disposed, and as the means for switching, a mechanism is widely used such that, in the vicinity of the dead end of the piston stroke, a cushion ring disposed at a distal end of a piston is fitted in a cushion packing at a spout portion in a recess part having the main discharge system formed in a head cover of a cylinder, by which the main discharge system is closed, and the compressed air sealed in the pressure chamber is gradually discharged to the outside through the cushion discharge system opened into the discharge-side pressure chamber.
On the other hand, in the one disclosed in Patent Document 1, a bypass opening/closing valve as means for switching the main discharge system to the cushion discharge system in the vicinity of the dead end of the piston stroke is disposed in a cushion unit disposed on the outside of a body (main body), and the bypass opening/closing valve is operated by a stroke adjusting bolt disposed on a stopper plate on a table driven in synchronization with the piston.
However, in either case, with this type of air cushion mechanisms, since the main discharge system is switched to the cushion discharge system in the vicinity of the dead end of the piston stroke, though a cushion-operation start position of the piston can be adjusted, a final stop position of the piston is set on the basis of a structure in the vicinity of a stroke end of the body, and the stop position of the piston stopped in a buffering manner cannot be set arbitrarily unless the internal structure of the body is changed.
In addition, the prior-art air cushion mechanism is configured so that the piston is stopped in a buffering manner by the internal structure of the body, and in order to stop the piston in a pneumatic cylinder not provided with an air cushion mechanism in a buffering manner, use of a damper made up of a viscoelastic body with relatively small impact absorbing capability has been an only available idea.